Selectively locking polyaxial screw

ABSTRACT

The present disclosure generally relates to pedicle screws that can selectively lock polyaxial motion of a receiver head with a locking cap. The locking cap can allow locking of the polyaxial motion of the receiver member relative to the spherical head of the bone shank without having a rod placed in the rod slot of the receiver member. This can enable placement of the head of the pedicle screw in a desired position and orientation, locking the head in the desired position and orientation, and performing a maneuver, such as derotation, without a rod in place or any extra motion between the receiver member and the bone shank. In some embodiments, actuation of the locking cap can be achieved by rotating the locking cap relative to the receiver member, where rotation of the locking cap causes corresponding axial translation of the locking cap relative to the receiver member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.63/157,384, entitled “Selectively Locking Polyaxial Screw,” filed onMar. 5, 2021. The entire contents of this application are herebyincorporated by reference in their entirety.

FIELD

This disclosure relates generally to surgical instruments and methods ofuse, and, more particularly, to a bone anchor that uses a locking cap toselectively lock polyaxial movement of a receiver member head of thebone anchor relative to a shank without having a spinal rod placed inthe receiver member.

BACKGROUND

During spine surgery, such as procedures to correct deformities in thespine, fixation constructs are often assembled to hold the spine in adesired shape. Such constructs often include a plurality of implantedbone anchors or pedicle screws along multiple vertebrae and a connectingspinal fixation element, such as a rod, that is received within areceiving member or head of each of the pedicle screws and secured usinga set screw. In many cases, the pedicle screws are first implanted inthe vertebrae, a rod is then positioned relative to the bone anchorheads, and set screws applied to secure the rod relative to each pediclescrew.

Current pedicle screw designs utilize various set screw locking methods.Single set screw designs allow a surgeon to lock polyaxial motion of thereceiver head relative to the bone shank and constrain the rod withinthe receiver head in one step of locking the set screw. In dual setscrew designs, a surgeon can lock polyaxial motion of the receiver headrelative to the bone shank by tightening an outer portion of a dual setscrew that contacts extended arms of a compression cap that reach aroundthe rod to allow polyaxial movement locking without locking the rodagainst movement. The surgeon then has the flexibility to separatelylock the rod relative to the receiver head by tightening an innerportion of the dual set screw that contacts the rod. Both the single setscrew and dual set screw designs can require the rod to be placed in thereceiver member of the pedicle screw prior to any polyaxial lockingbecause the rod cannot be placed into the receiver head in a top-loadingfashion after the set screw is threaded into the receiver head. That is,the standard pedicle screw transfers force from a set screw disposedproximal to a rod seat of the receiver member through one or more of acompression cap and a rod to the spherical head of the bone shank tolock against polyaxial motion of the bone shank relative to the receiverhead of the pedicle screw.

There is a need for improved bone anchors that provide greaterflexibility in selectively locking movement of a receiver member headrelative to a shank.

SUMMARY

The present disclosure generally relates to a pedicle screw that canselectively lock polyaxial motion of a receiver head relative to a screwshank with a locking cap used in lieu of a conventional compression capthat transfers forces from a set screw and rod to achieve such a lock.The locking cap can allow a surgeon to selectively lock the polyaxialmotion of the receiver member relative to the spherical head of the boneshank without having a rod placed in the rod slot of the receiver memberand/or a set screw coupled to the receiver member. The instantlydisclosed pedicle screw an prevent toggle of the receiver member duringa manipulation prior to set screw tightening (e.g., during a derotationmaneuver, etc.). When unlocked, the receiver member can move polyaxiallyrelative to the bone shank and can toggle during manipulation of thespine due to the lack of a locked connection between the head and theshank. Use of the locking cap can enable the surgeon to place the headof the pedicle screw in a desired position and orientation, lock thehead in the desired position and orientation, and perform a maneuver,such as derotation, without a rod in place or any extra motion betweenthe receiver member and the bone shank.

In one aspect, a bone screw assembly is provided that includes athreaded shank having a proximal head portion, a receiver memberdisposed around the proximal head portion such that a distal portion ofthe threaded shank extends through a hole formed in a distal end of thereceiver member, and a locking cap disposed in the receiver memberproximal to the proximal head portion of the threaded shank. The lockingcap can include one or more projections formed on an outer surfacethereof that can be disposed within a thread form on an interior surfaceof the receiver member. The locking cap can move between an unlockedconfiguration, in which the receiver member can move polyaxiallyrelative to the threaded shank, and a locked configuration, in which thereceiver member is prevented from moving relative to the threaded shank.The interior surface of the receiver member can include a non-threadedportion proximal to the thread form that receives the one or morelocking cap projections.

Any of a variety of alternative or additional features can be includedand are considered within the scope of the present disclosure. Forexample, in some embodiments, the non-threaded portion can be disposedbetween the thread form and a second threaded portion formed along aproximal end portion of the interior surface of the receiver member. Thethread form can include one or more keyways that intersect the threadform and extend axially along the interior surface of the receivermember to facilitate movement of the locking cap projections into thethread form. The keyways can intersect with a proximal-facing surface ofa U-shaped recess formed in the receiver member.

In certain embodiments, the locking cap can contact the proximal headportion of the threaded shank when in the locked configuration. In someembodiments, the locking cap can rotate a half turn to move from theunlocked configuration to the locked configuration. In some embodiments,the locking cap can further include a drive feature on a proximalsurface thereof. The locking cap can include two opposed projections insome embodiments. A distal-facing surface of the locking cap can have aprofile complementary to a shape of the proximal head portion of thethreaded shank. The proximal head portion of the threaded shank can havea spherical shape in some embodiments.

In some embodiments, the bone screw assembly can further include aspring clip seated within a groove formed in the interior surface of thereceiver member and configured to impart a drag force to the proximalhead portion of the threaded shank. In certain embodiments, the assemblycan further include a spinal fixation rod disposed within a U-shapedrecess formed in the receiver member proximal to the locking cap, and aset screw threadably coupled to the receiver member proximal to thespinal fixation rod. The spinal fixation rod can contact the locking capand the set screw can contact the spinal fixation rod.

In another aspect, a surgical method is provided that includes disposinga threaded shank within a receiver member such that the threaded shankand receiver member can move polyaxially relative to one another, anddistally advancing a locking cap into the receiver member through aproximal-facing opening past a non-threaded portion of an interiorsurface of the receiver member such that one or more projections formedon an exterior surface of the locking cap pass through one or morekeyways formed in the interior surface of the locking cap and pass intoa thread form in the interior surface of the receiver member. The methodcan further include rotating the locking cap to move between an unlockedconfiguration, in which the receiver member can move polyaxiallyrelative to the threaded shank, and a locked configuration, in which thereceiver member is prevented from moving relative to the threaded shank.

As with the instruments described above, the methods disclosed hereincan include any of a variety of additional or alternative steps that areconsidered within the scope of the present disclosure. In someembodiments, for example, the method further includes implanting thethreaded shank in a patient. In some embodiments, the threaded shank canbe implanted in a vertebra.

In certain embodiments, the method can further include performing any ofa derotation maneuver or a distraction maneuver after rotating thelocking cap to move to the locked configuration. In some embodiments,the method can further include placing a spinal fixation rod within aU-shaped recess of the receiver member after rotating the locking cap tomove to the locked configuration. Moreover, the method can furtherinclude threading a set screw into a threaded proximal end portion ofthe interior surface of the receiver member such that the set screwcontacts the spinal fixation rod and the spinal fixation rod contactsthe locking cap.

Any of the features or variations described herein can be applied to anyparticular aspect or embodiment of the present disclosure in a number ofdifferent combinations. The absence of explicit recitation of anyparticular combination is due solely to avoiding unnecessary length orrepetition.

BRIEF DESCRIPTION OF THE DRAWINGS

The aspects and embodiments of the present disclosure can be more fullyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings, in which:

FIG. 1 is a perspective view of one embodiment of a selectively lockingpolyaxial screw of the present disclosure;

FIG. 2 is an exploded perspective view of the selectively lockingpolyaxial screw of FIG. 1;

FIG. 3A is a top perspective view of the locking cap of the selectivelylocking polyaxial screw of FIG. 1;

FIG. 3B is a side perspective view of the locking cap of FIG. 3A;

FIG. 3C is a side cross-sectional view of the locking cap of FIG. 3A;

FIG. 4 is a top perspective view of the locking cap coupled to thereceiver member of the selectively locking polyaxial screw of FIG. 1;

FIG. 5 is a side perspective cross-sectional view of the receiver memberof FIG. 4 as taken along the line A-A;

FIG. 6 is a side perspective cross-sectional detail view of the receivermember of FIG. 4 as taken along the line B-B;

FIG. 7 is a perspective view of the selectively locking polyaxial screwof FIG. 1 in an unlocked configuration;

FIG. 8 is a perspective view of the selectively locking polyaxial screwof FIG. 1 with a driver coupled thereto;

FIG. 9 is a perspective view of the selectively locking polyaxial screwof FIG. 1 in a locked configuration;

FIG. 10 is a side cross-sectional view of the receiver member, lockingcap, and bone shank of the polyaxial screw of FIG. 1;

FIG. 11 is a side cross-sectional view of the assembly of FIG. 10 with aspinal rod and set screw disposed therein;

FIG. 12 is a perspective view of one embodiment of a derotation maneuverperformed by selectively locking pedicle screws against polyaxialmovement and manipulating vertebrae using the implanted pedicle screws;

FIG. 13 is a transverse plane cross-sectional view of the maneuver ofFIG. 12;

FIG. 14 is a sagittal plane view of one embodiment of a parallelcompression/distraction maneuver using forceps and implanted pediclescrews to adjust relative positions of the vertebrae;

FIG. 15 is a sagittal plane view of another embodiment of a parallelcompression/distraction movement; and

FIG. 16 is sagittal plane cross-sectional view of one embodiment of atrauma-correction maneuver.

DETAILED DESCRIPTION

Certain exemplary embodiments will now be described to provide anoverall understanding of the principles of the structure, function,manufacture, and use of the devices, systems, and methods disclosedherein. One or more examples of these embodiments are illustrated in theaccompanying drawings. The devices, systems, and methods specificallydescribed herein and illustrated in the accompanying drawings arenon-limiting embodiments. The features illustrated or described inconnection with one embodiment may be combined with the features ofother embodiments. Such modifications and variations are intended to beincluded within the scope of the present disclosure. Additionally, tothe extent that linear, circular, or other dimensions are used in thedescription of the disclosed devices and methods, such dimensions arenot intended to limit the types of shapes that can be used inconjunction with such devices and methods. Equivalents to suchdimensions can be determined for different geometric shapes, etc.Further, like-numbered components of the embodiments can generally havesimilar features. Still further, sizes and shapes of the devices, andthe components thereof, can depend at least on the anatomy of thesubject in which the devices will be used, the size and shape of objectswith which the devices will be used, and the methods and procedures inwhich the devices will be used.

The present disclosure generally relates to a pedicle screw design thatcan selectively lock polyaxial motion of a receiver head relative to ascrew shank with a locking cap used in lieu of a conventionalcompression cap that transfers forces from a set screw and rod toachieve such a lock. The locking cap can allow a surgeon to selectivelylock the polyaxial motion of the receiver member relative to thespherical head of the bone shank without having a rod placed in the rodslot of the receiver member. Moreover, the instantly disclosed pediclescrew prevents toggle of the receiver member during a manipulation priorto set screw tightening (e.g., during a derotation maneuver, etc.). Whenunlocked, the receiver member can move polyaxially relative to the boneshank and can toggle during a manipulation of the spine due to the lackof a locked connection between the head and the shank. Use of thelocking cap enables placement of the head of the pedicle screw in adesired position and orientation, locking the head in the desiredposition and orientation, and performing a maneuver, such as derotation,without a rod in place or any extra motion between the receiver memberand the bone shank.

For example, after implantation of a pedicle screw, the receiver membercan be moved into a desired position and a driver can be used to tightenthe locking cap to lock the polyaxial head to the shank and allow formanipulation of the vertebra in which the screw is implanted through thepedicle screw without the rod in place. This can be advantageous incertain cases, e.g., in cases where the spine is deformed such that arod cannot be placed prior to deformity correction. Following rodplacement, a standard set screw can be inserted into the receiver memberand the implant can function like a standard pedicle screw where thespinal fixation rod transfers load from the set screw to the locking capand bone shank to provide final locking of the pedicle screw.

FIGS. 1 and 2 illustrate one embodiment of a selectively lockingpolyaxial screw 100. As shown, the screw can include a bone shank 102received in a distal opening of a receiver member 104 to couple thereto.The coupling between the shank and the receiver member 104 can occur byengaging a spherical head 202 of the bone shank with a locking cap or alocking screw 106. The locking cap 106 can engage a portion of thereceiver member to lock the receiver member in a desired orientationrelative to the shank 102 prior to insertion of a spinal rod. Afterlocking, a spinal rod or another surgical device can be advanceddistally to sit on a proximal end of the locking cap 106 and a set screw108 can be advanced between the arms of the receiver member 104 to lockthe spinal rod within the pedicle screw (see FIG. 11).

As shown in FIG. 2, to assemble the screw 100 a spring clip 204 can betop loaded or advanced distally into an interior of the receiver member104 until it sits within a groove formed therein (see FIGS. 5 and 6).The shank 102 can then be top loaded or advanced distally into theinterior of the receiver member 104 until the distal bone-engagingportion of the shank 102 extends through a hole formed in the distal endof the receiver member 104, the proximal spherical head 202 is seatedwithin a polyaxial seat formed in a distal end of the receiver member104, and the spring clip 204 is frictionally engaged with the sphericalhead of the bone shank to provide a drag force resisting movement of thereceiver member relative to the bone shank 102. The locking cap 106 canthen be top loaded or advanced distally into the interior of thereceiver member 104, as described in more detail below. Finally, a rodcan be top loaded or advanced distally into the U-shaped recess formedbetween spaced apart arms of the receiver member 104 and the set screw108 can be top loaded or advanced distally to engage with threads formedalong a proximal interior portion of the receiver member to achievefinal locking of the screw and rod.

FIGS. 1 and 2 also illustrate additional features of the receiver member104, including the presence of unilateral holding features 110 at thelateral ends of each spaced apart arm of the receiver member 104. Thesefeatures can interface with a unilateral holding instrument to allowgripping of the receiver member 104 in a manner that does not obstructthe proximal end opening of the U-shaped recess in the receiver member.This can be advantageous in connection with the selective lockingfeatures described herein, as any of a variety of manipulations can beperformed without a rod placed in the receiver member 104 and whileallowing the subsequent placement of such a rod using a top loading ordistal advancement motion. Also shown is a groove or notch 112 formedaround an outer surface of the spaced apart arms along a proximalportion of the receiver member 104, which can be utilized to couple anyof a variety of instruments to the receiver head. Further, a rockerrecess 114 is visible and shown intersecting the groove 112. A secondrocker recess (not visible) can be formed on an opposite side of thereceiver member and these recesses can be utilized to couple thereceiver member to another surgical instrument, such as a rocker forkrod reducing instrument. Further details regarding other features ofpedicle screws that can be included can be found in U.S. Pat. Nos.10,039,578 and 10,299,839, as well as U.S. Provisional Appl. No.63/157,362, entitled “Multi-Feature Polyaxial Screw” and filed on Mar.5, 2021, and U.S. application Ser. No. 17/685,359, entitled“Multi-Feature Polyaxial Screw,” filed on Mar. 2, 2022, and claimingpriority to the previously-noted provisional application. The entirecontents of each of these applications are incorporated by referenceherein.

FIGS. 3A-3C illustrate an example embodiment of the locking cap 106. Asmentioned above, the locking cap 106 can be used in place of aconventional compression cap or saddle within the pedicle screw toselectively lock polyaxial movement of the shank 102 relative to thereceiver member 104. As shown, the locking cap 106 can include acylindrical body 302 having a channel 304 formed therein. At least aportion of the channel 304, e.g., the proximal end, can include a drivefeature 305 for receiving one or more instruments therethrough that canrotate the locking cap. Example drive features can include hex drivefeatures, square drive features, lobed drive features, etc. The driverused to rotate the locking cap 106 can be a screwdriver or similarcomponent configured to rotate the locking cap 106 relative to thereceiver member 104. As explained in more detail below, rotation of thelocking cap 106 relative to the receiver member 104 can cause axialtranslation of the locking cap 106 due to interaction of a thread formin the receiver member 104 guiding a projection formed on the lockingcap 106.

The locking cap 106 can include one or more projections or ears 306extending from an outer surface of the cylindrical body 302. As shown,the projections 306 can extend in opposite directions from the outersurface of the body 302.

While two projections 306 are shown, an alternative number can beutilized (e.g., one, three, or more). In an embodiment where a largernumber of projections 306 are utilized, they can be spaced evenly aroundthe circumference of the body 302. Further, in some embodiments, thecylindrical body 302 of the locking cap 106 can include a continuousthread form extending around on an outer surface thereof in place ofdiscrete projections.

The one or more projections 306 can have varying dimensions, includingvarious widths W extending around the circumference of the cylindricalbody 302, radial depths RD extending outward from the outer surface ofthe cylindrical body 302, and axial depths AD extending along alongitudinal axis of the cylindrical body 302. Further, the one or moreprojections can have varying shapes, including, for example, aproximal-facing surface 1002 that extends substantially perpendicularlyfrom the outer surface of the cylindrical body 302, and a distal-facingsurface 1003 that is angled obliquely relative to the outer surface ofthe cylindrical body 302. The angle A between the distal-facing surface1003 and the outer surface of the cylindrical body 302 can vary and, insome embodiments, can be configured such that a radial measurement tothe distal-facing surface 1003 increases in a proximal direction from adistal-most edge of the projection 306 (e.g., an angle A greater than90° as shown) to facilitate introduction of the locking cap 106 into thereceiver member 104.

The various dimensions of each projection 306 can vary in differentembodiments, e.g., based on a circumference of the locking cap 106, thenumber of projections, etc. Generally speaking, it can be desirable tomaximize a size of each projection 306 to maximize the strength thereof,but this must be balanced against a competing interest to minimize asize of any keyway or cutout formed in the receiver member 104 thatreceives each projection 306 during assembly. In some embodiments, awidth W of a projection 306 can be selected to be less than a width of arod-slot RSW (see FIG. 4) such that any keyway 402 formed in a receivermember 104 can have a keyway width KW that is less than the rod-slotwidth RSW. This can minimize material that is removed from the receivermember 104 when forming the keyway 402, thereby maximizing strength ofthe receiver member.

In some embodiments, the width W of each projection can extend through aradial arc of less than about 90°. In some embodiments, the width W ofeach projection can extend through a radial arc between about 45° andabout 90° (resulting in between about ⅛ to about ¼ of a turn of the cap106 to engage the projections with the receiver member 104). In someembodiments, the width W of each projection can extend through a radialarc of less than about 45°. Exact dimensions of the width W, radialdepth RD, axial depth AD, and angle A of the distal-facing surface 1003of each projection 306 can be varied based on a number of factors, suchas overall screw size, number of projections, etc.

FIGS. 4-6 illustrate the receiver member 104 interior surfaces andinteraction with the locking cap 106 in greater detail. As shown inFIGS. 5 and 6, which represent cross sectional views of the receivermember as taken along the lines A-A and B-B, respectively, shown in FIG.4, the receiver member interior surface can include a proximal portionhaving a thread form 502 formed therein to receive a set screw 108. Afurther thread form 504 can be formed at a more distal location adjacenta distal end of the U-shaped recess defined by the spaced apart arms ofthe receiver member. Between the two thread forms, the receiver member104 can include a smooth intermediate inner surface 506. Including theintermediate inner surface 506 can be advantageous because the absenceof any thread form or other feature requiring removal of material canallow the receiver member wall to be at a maximum thickness, therebymaximizing stiffness of the receiver head. Also shown in FIGS. 5 and 6are the groove 508 that receives the spring clip 204 and the polyaxialseat 510 that receives the spherical head 202 of the bone shank anddefines the hole 512 formed in the distal end of the receiver member.

The thread form 504 that receives the protrusions 306 or other threadingfeatures of the locking cap 302 can allow the locking cap to ride alonga surface thereof and control its position along a proximal-distal axisA1 (see FIG. 2), thereby controlling the frictional lock between thelocking cap 106 and the head of the shank. The thread form 504 caninclude a variety of pitches based on the desired axial translation ofthe locking cap 106. The thread form 504 can also include a variety ofrotations, including, in some embodiments, a single rotation or otherconfiguration to allow quick locking or actuation of the locking cap 106with one or less than one complete rotation of a driver. For example, insome embodiments the thread form 504 can be configured such that any ofa quarter turn, half turn, or three-quarter turn of a driver iseffective to actuate the locking cap 106 and selectively lock outpolyaxial motion of a receiver head relative to a bone shank. In theillustrated embodiment, for example, a half turn of a driver iseffective to actuate the locking cap 106.

The locking cap 106 can be inserted into the receiver member 104 bypassing it distally from a proximal end of the receiver member such thatthe projections 306 are aligned with one or more keyways or slots 402formed therein. The keyways 402 can allow the locking cap 106 to betranslated distally from a proximal end of the receiver member 104 allthe way to the thread form 504 without requiring any rotation of thelocking cap 106. This can allow rapid assembly of the locking cap 106 tothe receiver member 104 without requiring numerous turns of an actuatingdriver, which may not be possible if, for example, the entire interiorsurface of the receiver member included threads. The keyways or slots402 can have a width KW sufficient to receive the width W of eachprojection 306 formed on the locking cap 106.

Once the locking cap 106 is advanced distally such that the projections306 are received within the keyways 402 and aligned with the thread form504, a driver can be used to rotate the locking cap 106 such that theprojections 306 ride within the thread form 504 and control the furtheraxial translation of the locking cap. The thread form 504 can beconfigured such that, as the projections 306 ride along the thread form504 during rotation of the locking cap 106, the locking cap moves froman unlocked configuration, in which relative movement between thereceiver member 104 and bone shank 102 are permitted, to a lockedconfiguration, in which movement between the receiver member 104 and thebone shank 102 is prevented by frictional engagement between the lockingcap distal surface 308 (see FIG. 3) and the spherical head 202 of thebone shank.

FIGS. 7-9 illustrate one embodiment of operation of the polyaxial screw100. In FIG. 7, the screw is shown in an unlocked configuration wherepolyaxial movement of the receiver member 104 relative to the bone shank102 is permitted. This is because the locking cap 106 is positionedaxially in a manner that it either does not contact the spherical headof the bone shank 102 or does so in a manner that does not exertsufficient frictional force to lock the position of the receiver member104 relative to the bone shank 102. Note that it is possible to positionthe locking cap 106 in a manner that provides some degree of frictionalengagement with the bone shank and therefore provides a provisional lockof the receiver member position that can be overcome by a user. In someembodiments, the drag clip 204 can provide such a provisional lockingforce in place of, or in addition to, the locking cap 106.

In FIG. 8, a driver instrument 200 is shown actuating the locking cap106 by rotating it relative to the receiver member 104. As the driverinstrument 200 rotates the locking cap 106, the projections 306 on thelocking cap 106 with ride within the thread form 504 of the receivermember 104 and the locking cap 106 can move distally relative to thereceiver member 104 in accordance with the axial pitch of the threadform 504. As the locking cap 106 advances distally during actuation, itcan exert a greater frictional force on the spherical head of the boneshank 102 and effect a selective lock against polyaxial movement of thereceiver member 104 relative to the bone shank 102. The driverinstrument 200 can engage the locking cap 106 via the drive feature 305on the proximal end of the locking cap 106. For example, the driver 200can include a distal drive feature (not shown) that corresponds to thedrive feature 305 on the proximal end of the locking cap 106 to allowrotation of the locking cap 106 relative to the polyaxial screw 100. Thelocking cap 106 can be rotated approximately a quarter turn, a halfturn, a full turn, or more to actuate the locking cap 106.

FIG. 9 illustrates the screw 100 in a locked configuration once thelocking cap 106 has been fully actuated. In such a configuration,polyaxial movement of the receiver member 104 relative to the bone shank102 is prevented by the frictional engagement of the locking cap 106 andspherical head 202 of the bone shank 102. FIG. 10 illustrates across-sectional view of the receiver member 104, locking cap 106, andbone shank 102 with spherical head 202. This view illustrates theproximal-facing surfaces 1002 of the projections 306 engagingdistal-facing surfaces 1004 of the thread form 504 in order to urge thelocking cap 106 distally (as shown by arrows 1006) and impart africtional force onto the spherical head 202 of the bone shank. Asmentioned above, unlike a conventional compression cap which transfersforce from a set screw and rod to the shank to lock the polyaxialmotion, the locking cap 106 can lock the receiver member 104 relative tothe shank without a rod or set screw in place. This is because theprojections of the locking cap 106 can form a shoulder that abuts asurface of the thread form 504 to prevent proximal translation of thelocking cap 106 relative to the receiver member 104. A distal surface308 of the locking cap can engage the spherical head 202 of the boneshank to force a coupling between the locking cap and the spherical headof the shank.

Note also that a height of the thread form 504 can be greater than aheight of the projections 306 such that additional distal translation ofthe locking cap 106 is possible. Such additional distal translation canbe achieved using a set screw and rod force transfer in the manner of aconventional polyaxial screw, as shown in FIG. 11. As a result, thelocking cap 106 provides a further advantage in that it can function inthe same manner as a conventional compression cap after a rod and setscrew are placed in the receiver member U-shaped opening. That is, afinal locking of the polyaxial screw, with potentially even greaterlocking force than can be achieved with the locking cap 106, can beachieved without requiring further direct manipulation of the lockingcap 106. A spinal fixation rod 1102 and set screw 108 can be placed inthe U-shaped recess of the receiver member 104 and the set screwtightened. As the set screw bears distally down on the rod, the rod canbear distally down on the locking cap 106, as shown by arrow 1104. Giventhe freedom for additional distal translation provided by the differencein height between the thread form 504 and the locking cap projections306, the locking cap can be urged distally by the force from the rod andset screw, thereby engaging a distal end 308 of the locking cap 106 withthe spherical head 202 of the bone shank 102. With such a configuration,the set screw and rod can assume the load for locking the screw andrelieve any force exerted between the proximal-facing surfaces 1002 ofthe locking cap projections and the distal-facing surfaces 1004 of thethread form 504.

FIGS. 12-16 illustrate various procedures that can be performed usingthe polyaxial screws of the present disclosure. For example, FIGS. 12and 13 show derotation maneuvers that can be performed by selectivelylocking pedicle screws against polyaxial movement and pulling orrotating vertebrae using the implanted pedicle screws. For example, FIG.12 illustrates a perspective view of a surgeon or other usermanipulating a group of vertebrae 1202 by exerting forces from theirhand 1204 onto a group of implanted pedicle screws 1206 implanted in thevertebrae, e.g., to move the vertebrae in the direction of arrows 1208,1209. When performing such maneuvers, it can be desirable to lock one ormore implanted pedicle screws against polyaxial movement that can createtoggling of a receiver member relative to an implanted screw shank whenforce is applied thereto. FIG. 13 illustrates a transverse plane view ofthe maneuver of FIG. 12. In the maneuvers shown in FIGS. 12 and 13,however, a spinal fixation rod 1210 is shown placed in the U-shapedrecess of each pedicle screw and instrumentation 1212 is attachedthereto that obstructs the proximal end opening of the U-shaped recessof each pedicle screw 1206. Accordingly, the selectively lockingpolyaxial screws disclosed herein can provide additional advantages insimilar maneuvers, since they can be performed prior to rod and/or setscrew placement and can utilize extension instrumentation that couplesto the receiver members on only one side thereof (e.g., using unilateralattachment feature 110) to preserve access to the proximal end of theU-shaped opening. Examples of such extension instrumentation areprovided in U.S. Pat. No. 10,966,762, the entire contents of which areincorporated by reference herein.

FIGS. 14-16 illustrate various distraction, compression, andtrauma-correction maneuvers that can also be facilitated using theselective locking screws disclosed herein. In such maneuvers, implantedpedicle screws 1402, 1502, 1602 can be locked against polyaxial movementand forceps 1404 or other extension instrumentation can be coupled tothe screws and utilized to exert forces that adjust relative positionsof vertebrae, e.g., increase or decrease a distance or angletherebetween, etc., as shown by arrows 1401, 1501, 1601. In suchembodiments, one or more surgical instruments can be attached to thescrews and rotated and/or translated relative to one another so as toalign the vertebrae in a desired direction. Across a variety ofmaneuvers, selectively locking screws as disclosed herein can providesurgeons with flexibility to perform maneuvers before or after rodplacement, which can be a significant advantage over conventionalinstrumentation and techniques.

The instruments disclosed herein can be constructed from any of avariety of known materials. Example materials include those which aresuitable for use in surgical applications, including metals such asstainless steel, titanium, nickel, cobalt-chromium, or alloys andcombinations thereof, polymers such as PEEK, ceramics, carbon fiber, andso forth. Further, various methods of manufacturing can be utilized,including 3D printing or other additive manufacturing techniques, aswell as more conventional manufacturing techniques, including molding,stamping, casting, machining, etc.

The devices and methods disclosed herein can be used inminimally-invasive surgery and/or open surgery. While the devices andmethods disclosed herein are generally described in the context ofsurgery on a human patient, it will be appreciated that the methods anddevices disclosed herein can be used in any of a variety of surgicalprocedures with any human or animal subject, or in non-surgicalprocedures.

The devices disclosed herein can be designed to be disposed of after asingle use, or they can be designed to be used multiple times. In eithercase, however, the device can be reconditioned for reuse after at leastone use. Reconditioning can include any combination of the steps ofdisassembly, followed by cleaning or replacement of particular pieces,and subsequent reassembly. In particular, a device or component can bedisassembled, and any number of the particular pieces or parts thereofcan be selectively replaced or removed in any combination. Upon cleaningand/or replacement of particular parts, the device or component can bereassembled for subsequent use either at a reconditioning facility, orby a surgical team immediately prior to a surgical procedure.Reconditioning of a device or component can utilize a variety oftechniques for disassembly, cleaning/replacement, and reassembly. Use ofsuch techniques, and the resulting reconditioned device, are all withinthe scope of the present disclosure.

The devices described herein can be processed before use in a surgicalprocedure. For example, a new or used instrument or component can beobtained and, if necessary, cleaned. The instrument or component can besterilized. In one sterilization technique, the instrument or componentcan be placed in a closed and sealed container, such as a plastic orTYVEK bag. The container and its contents can be placed in a field ofradiation that can penetrate the container, such as gamma radiation,x-rays, or high-energy electrons. The radiation can kill bacteria on theinstrument or component and in the container. The sterilized instrumentor component can then be stored in the sterile container. The sealedcontainer can keep the instrument or component sterile until it isopened in the medical facility. Other forms of sterilization are alsopossible, including beta or other forms of radiation, ethylene oxide,steam, or a liquid bath (e.g., cold soak). Certain forms ofsterilization may be better suited to use with different portions of thedevice or component due to the materials utilized, the presence ofelectrical components, etc.

In this disclosure, phrases such as “at least one of” or “one or moreof” may occur followed by a conjunctive list of elements or features.The term “and/or” may also occur in a list of two or more elements orfeatures. Unless otherwise implicitly or explicitly contradicted by thecontext in which it is used, such a phrase is intended to mean any ofthe listed elements or features individually or any of the recitedelements or features in combination with any of the other recitedelements or features. For example, the phrases “at least one of A andB,” “one or more of A and B,” and “A and/or B” are each intended to mean“A alone, B alone, or A and B together.” A similar interpretation isalso intended for lists including three or more items. For example, thephrases “at least one of A, B, and C,” “one or more of A, B, and C,” and“A, B, and/or C” are each intended to mean “A alone, B alone, C alone, Aand B together, A and C together, B and C together, or A and B and Ctogether.” In addition, use of the term “based on,” is intended to mean,“based at least in part on,” such that an un-recited feature or elementis also permissible.

Further features and advantages based on the above-described embodimentsare possible and within the scope of the present disclosure.Accordingly, the disclosure is not to be limited by what has beenparticularly shown and described. All publications and references citedherein are incorporated by reference in their entirety, except for anydefinitions, subject matter disclaimers, or disavowals, and except tothe extent that the incorporated material is inconsistent with theexpress disclosure herein, in which case the language in this disclosurecontrols.

Examples of the above-described embodiments can include the following:

-   -   1. A bone screw assembly, comprising:        -   a threaded shank having a proximal head portion;        -   a receiver member disposed around the proximal head portion            such that a distal portion of the threaded shank extends            through a hole formed in a distal end of the receiver            member; and        -   a locking cap disposed in the receiver member proximal to            the proximal head portion of the threaded shank, the locking            cap including one or more projections formed on an outer            surface thereof that are disposed within a thread form on an            interior surface of the receiver member;        -   wherein the locking cap moves between an unlocked            configuration, in which the receiver member can move            polyaxially relative to the threaded shank, and a locked            configuration, in which the receiver member is prevented            from moving relative to the threaded shank;        -   wherein the interior surface of the receiver member includes            a non-threaded portion proximal to the thread form that            receives the one or more locking cap projections.    -   2. The assembly of claim 1, wherein the non-threaded portion is        disposed between the thread form and a second threaded portion        formed along a proximal end portion of the interior surface of        the receiver member.    -   3. The assembly of any of claims 1 to 2, wherein the thread form        includes one or more keyways that intersect the thread form and        extend axially along the interior surface of the receiver member        to facilitate movement of the locking cap projections into the        thread form.    -   4. The assembly of claim 3, wherein the keyways intersect with a        proximal-facing surface of a U-shaped recess formed in the        receiver member.    -   5. The assembly of any of claims 1 to 4, wherein the locking cap        contacts the proximal head portion of the threaded shank when in        the locked configuration.    -   6. The assembly of any of claims 1 to 5, wherein the locking cap        rotates a half turn to move from the unlocked configuration to        the locked configuration.    -   7. The assembly of any of claims 1 to 6, wherein the locking cap        further comprises a drive feature on a proximal surface thereof.    -   8. The assembly of any of claims 1 to 7, further comprising a        spring clip seated within a groove formed in the interior        surface of the receiver member and configured to impart a drag        force to the proximal head portion of the threaded shank.    -   9. The assembly of any of claims 1 to 8, further comprising:        -   a spinal fixation rod disposed within a U-shaped recess            formed in the receiver member proximal to the locking cap;            and        -   a set screw threadably coupled to the receiver member            proximal to the spinal fixation rod.    -   10. The assembly of claim 9, wherein the spinal fixation rod        contacts the locking cap and the set screw contacts the spinal        fixation rod.    -   11. The assembly of any of claims 1 to 10, wherein the locking        cap includes two opposed projections.    -   12. The assembly of any of claims 1 to 11, wherein a        distal-facing surface of the locking cap has a profile        complementary to a shape of the proximal head portion of the        threaded shank.    -   13. The assembly of claim 12, wherein the proximal head portion        of the threaded shank has a spherical shape.    -   14. A surgical method, comprising:        -   disposing a threaded shank within a receiver member such            that the threaded shank and receiver member can move            polyaxially relative to one another;        -   distally advancing a locking cap into the receiver member            through a proximal-facing opening past a non-threaded            portion of an interior surface of the receiver member such            that one or more projections formed on an exterior surface            of the locking cap pass through one or more keyways formed            in the interior surface of the locking cap and pass into a            thread form in the interior surface of the receiver member;            and        -   rotating the locking cap to move between an unlocked            configuration, in which the receiver member can move            polyaxially relative to the threaded shank, and a locked            configuration, in which the receiver member is prevented            from moving relative to the threaded shank.    -   15. The method of claim 14, further comprising implanting the        threaded shank in a patient.    -   16. The method of claim 15, wherein the threaded shank is        implanted in a vertebra.    -   17. The method of claim 16, further comprising performing any of        a derotation maneuver or a distraction maneuver after rotating        the locking cap to move to the locked configuration.    -   18. The method of any of claims 14 to 17, further comprising        placing a spinal fixation rod within a U-shaped recess of the        receiver member after rotating the locking cap to move to the        locked configuration.    -   19. The method of claim 18, further comprising threading a set        screw into a threaded proximal end portion of the interior        surface of the receiver member such that the set screw contacts        the spinal fixation rod and the spinal fixation rod contacts the        locking cap.

What is claimed is:
 1. A bone screw assembly, comprising: a threadedshank having a proximal head portion; a receiver member disposed aroundthe proximal head portion such that a distal portion of the threadedshank extends through a hole formed in a distal end of the receivermember; and a locking cap disposed in the receiver member proximal tothe proximal head portion of the threaded shank, the locking capincluding one or more projections formed on an outer surface thereofthat are disposed within a thread form on an interior surface of thereceiver member; wherein the locking cap moves between an unlockedconfiguration, in which the receiver member can move polyaxiallyrelative to the threaded shank, and a locked configuration, in which thereceiver member is prevented from moving relative to the threaded shank;wherein the interior surface of the receiver member includes anon-threaded portion proximal to the thread form that receives the oneor more locking cap projections.
 2. The assembly of claim 1, wherein thenon-threaded portion is disposed between the thread form and a secondthreaded portion formed along a proximal end portion of the interiorsurface of the receiver member.
 3. The assembly of claim 1, wherein thethread form includes one or more keyways that intersect the thread formand extend axially along the interior surface of the receiver member tofacilitate movement of the locking cap projections into the thread form.4. The assembly of claim 3, wherein the keyways intersect with aproximal-facing surface of a U-shaped recess formed in the receivermember.
 5. The assembly of claim 1, wherein the locking cap contacts theproximal head portion of the threaded shank when in the lockedconfiguration.
 6. The assembly of claim 1, wherein the locking caprotates a half turn to move from the unlocked configuration to thelocked configuration.
 7. The assembly of claim 1, wherein the lockingcap further comprises a drive feature on a proximal surface thereof. 8.The assembly of claim 1, further comprising a spring clip seated withina groove formed in the interior surface of the receiver member andconfigured to impart a drag force to the proximal head portion of thethreaded shank.
 9. The assembly of claim 1, further comprising: a spinalfixation rod disposed within a U-shaped recess formed in the receivermember proximal to the locking cap; and a set screw threadably coupledto the receiver member proximal to the spinal fixation rod.
 10. Theassembly of claim 9, wherein the spinal fixation rod contacts thelocking cap and the set screw contacts the spinal fixation rod.
 11. Theassembly of claim 1, wherein the locking cap includes two opposedprojections.
 12. The assembly of claim 1, wherein a distal-facingsurface of the locking cap has a profile complementary to a shape of theproximal head portion of the threaded shank.
 13. The assembly of claim12, wherein the proximal head portion of the threaded shank has aspherical shape.
 14. A surgical method, comprising: disposing a threadedshank within a receiver member such that the threaded shank and receivermember can move polyaxially relative to one another; distally advancinga locking cap into the receiver member through a proximal-facing openingpast a non-threaded portion of an interior surface of the receivermember such that one or more projections formed on an exterior surfaceof the locking cap pass through one or more keyways formed in theinterior surface of the locking cap and pass into a thread form in theinterior surface of the receiver member; and rotating the locking cap tomove between an unlocked configuration, in which the receiver member canmove polyaxially relative to the threaded shank, and a lockedconfiguration, in which the receiver member is prevented from movingrelative to the threaded shank.
 15. The method of claim 14, furthercomprising implanting the threaded shank in a patient.
 16. The method ofclaim 15, wherein the threaded shank is implanted in a vertebra.
 17. Themethod of claim 16, further comprising performing any of a derotationmaneuver or a distraction maneuver after rotating the locking cap tomove to the locked configuration.
 18. The method of claim 14, furthercomprising placing a spinal fixation rod within a U-shaped recess of thereceiver member after rotating the locking cap to move to the lockedconfiguration.
 19. The method of claim 18, further comprising threadinga set screw into a threaded proximal end portion of the interior surfaceof the receiver member such that the set screw contacts the spinalfixation rod and the spinal fixation rod contacts the locking cap.